What happened
On November 20, 1998, a pilot operating a Cessna 182Q, registration HB-CJK, departed from Speck-Fehraltorf airfield with the intention of flying over to Altenrhein. After performing pre-flight preparations, including clearing snow from the airframe and refueling with 95 liters of fuel, the pilot departed from runway 12. The flight initially proceeded normally, reaching an altitude of approximately 200 meters over Pfäffikersee.
During the cruise phase, the aircraft experienced a sudden drop in engine power, with RPM falling from 2400 to 2000 or lower. Although applying the carburetor heat provided a temporary improvement, a second, more significant power loss occurred near the eastern end of the lake, leaving the pilot unable to maintain flight. The pilot identified a field in the direction of the wind and attempted an emergency landing. The aircraft touched down on its main wheels at a high angle of attack. As the nose wheel made contact, it sank into the partially frozen ground, causing the aircraft to overturn.
The investigation
SUST examined the aircraft, the pilot's credentials, and the meteorological conditions at the time of the accident. The investigation confirmed that the pilot held a valid license and that the aircraft was properly maintained, with its last 100-hour inspection completed earlier that year. The aircraft's weight and balance were within limits, and no mechanical defects were found in the airframe or the Precision MA-4-5 carburetor during post-accident inspection.
Meteorological data revealed that the region was experiencing light snowfall with temperatures between -2°C and -2.5°C. The dew point was also low, creating atmospheric conditions conducive to icing. A subsequent test run of the engine on December 2, 1998, under similar temperature and humidity conditions, showed no signs of carburetor icing, though the investigation focused on the specific conditions present during the accident.
Findings
- The primary cause of the power loss was carburetor icing.
- Atmospheric conditions, characterized by light snow and specific temperature/dew point levels, likely triggered the ice formation.
- The pilot's decision to land in the available field was appropriate given the loss of power.
- The ground surface, while appearing suitable, was only superficially frozen and lacked the necessary load-bearing capacity to support the nose wheel upon touchdown.
- The aircraft overturned because the main wheels dug into the soft, frozen earth, causing the nose gear to sink and the plane to pitch forward.